Abstract

An optical sensor based on One-Dimensional photonic crystal (1D PhC) stack mode-gap cavity has been designed, fabricated and characterized. By introducing quadratically modulated width tapering structure, a waveguide coupled 1D PhC stack mode-gap cavity with calculated Q-factor 1.74 × 107 and an effective mode volume 1.48(λ/nSi)3 has been designed. This cavity has been used for sensing applications by immersing into water-ethanol mixture of different volume concentrations. Transmission measurement shows a quality factor as high as 27, 000 can be achieved for the cavity immersed in analytes. A sensitivity of 269nm/RIU has been demonstrated.

Influence of (a) Wx, (b) Wy(0) and (c) number of Gaussian mirror segments (NG) on the Q-factor and sensitivity of width-modulated stack cavity sensor;(d) Wavelength shift and variance of Q-factor over different background refractive indices.

(a) Measured transmission spectrum with estimated input power of about 6 μw. The dots are the experimental data and the line is the fit to Lorentzian lineshape. The full width at half maximum (FWHM) is about 58 pm; (b) The transmission spectrum taken as the cavity was immersed into water-ethanol mixture of different volume concentrations with estimated input power of about 180 μw (c) Wavelengths of the cavity mode in different background refractive indices; (d) Wavelengths of cavity mode in different background temperatures when the estimated input power is about 6 μw. The slope is about −0.025nm/°C.